1. Field of the Invention
The present invention relates to ophthalmic lenses, and more particularly to contact lenses incorporating features that enhance oxygen transmission to the cornea.
2. Discussion of the Related Art
Myopia or nearsightedness is an optical or refractive defect of the eye wherein rays of light from an image focus to a point before they reach the retina. Myopia generally occurs because the eyeball or globe is too long or the cornea is too steep. A minus powered spherical lens may be utilized to correct myopia. Hyperopia or farsightedness is an optical or refractive defect of the eye wherein rays of light from an image focus to a point behind the retina. Hyperopia generally occurs because the eyeball or globe is too short or the cornea is too flat. A plus powered spherical lens may be utilized to correct hyperopia. Astigmatism is an optical or refractive defect in which an individual's vision is blurred due to the inability of the eye to focus a point object into a focused image on the retina. Unlike myopia and/or hyperopia, astigmatism has nothing do to with globe size or cornea steepness, but rather it is caused by an abnormal curvature of the cornea. A perfect cornea is spherical whereas in an individual with astigmatism, the cornea is not spherical. In other words, the cornea is actually more curved or steeper in one direction than another, thereby causing an image to be stretched out rather than focused to a point. A cylindrical lens rather than a spherical lens may be utilized to resolve astigmatism.
Contact lenses may be utilized to correct myopia, hyperopia, astigmatism as well as other visual acuity defects. Contact lenses may also be utilized to enhance the natural appearance of the wearer's eyes. In other words, contact lenses may be colored or tinted to provide a variety of effects to the appearance of the eye. A number of different types of tinted contact lenses are currently available to enhance an individual's eye color or change it altogether. Contact lenses comprising cosmetic enhancement tints are designed to enhance ones natural eye color and are best suited for light-colored eyes such as blues, greens, hazels and grays. Contact lenses comprising opaque tints are designed to change the color of dark eyes. These lenses are patterned and are designed to cover the iris while providing a natural look. Contact lenses may also comprise visibility tints which are designed to make the lens visible during handling with no discernible effect on eye color.
Based upon the above, the primary functions of contact lenses are vision correction and/or enhancement, cosmetic enhancement and/or both vision correction and cosmetic enhancement. However, contact lenses are also preferably designed to ensure that sufficient levels of oxygen are supplied to the eye, specifically, the cornea, to promote cornea health and growth. An inadequate amount of oxygen supplied to the cornea may result in a number of negative effects on eye health, including edema. Soft contact lenses represented a significant improvement over hard contact lenses with respect to oxygen permeability; however, the amount of oxygen transmitted through a soft contact lens is limited by both the material oxygen permeability, Dk, and the material thickness, t. Accordingly, there exists a need for a soft contact lens that is comfortable to wear and allows more oxygen to easily and quickly diffuse therethrough. More particularly, while increased oxygen transmissibility can be achieved by reformulating a given material, there also exists a need for soft contact lenses with increased oxygen transmissibility utilizing existing and proven materials, for example, hydrogels and silicone-hydrogels.